Mortgage-Backed Securities - Investment Type (Details) - USD ($) $ in Thousands		Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		$ 5,975,467	$ 3,236,285
Amortized Cost		6,151,247	3,522,256
Fair Value		5,583,757	3,112,705
Amortized cost		1,164,265	1,288,269
Gross Unrealized Gain		1,275	507
Gross Unrealized Loss		(219,045)	(181,853)
Fair Value		946,495	1,106,923
Amortized Cost		4,986,982	2,233,987
Gross Unrealized Gain		0	0
Gross Unrealized Loss		(349,720)	(228,205)
Fair Value		4,637,262	2,005,782
Residential Mortgage Backed Securities [Member]
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		5,853,691	3,104,498
Amortized Cost		5,844,730	3,150,873
Fair Value		5,298,271	2,762,878
Amortized cost		914,900	977,624
Gross Unrealized Gain		0	0
Gross Unrealized Loss		(202,677)	(164,949)
Fair Value		712,223	812,675
Amortized Cost		4,929,830	2,173,249
Gross Unrealized Gain		0	0
Gross Unrealized Loss		(343,782)	(223,046)
Fair Value		4,586,048	1,950,203
Commercial Mortgage Backed Securities [Member]
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		121,617	131,578
Amortized Cost		122,171	132,333
Fair Value		112,396	124,690
Amortized cost		106,892	117,031
Gross Unrealized Gain		0	0
Gross Unrealized Loss		(7,791)	(6,474)
Fair Value		99,101	110,557
Amortized Cost		15,279	15,302
Gross Unrealized Gain		0	0
Gross Unrealized Loss		(1,984)	(1,169)
Fair Value		13,295	14,133
Interest-Only-Strip [Member]
Debt Securities, Trading and Available-for-sale [Abstract]
Amortized Cost	[1]	184,187	238,841
Fair Value	[1]	172,987	224,985
Amortized cost		142,314	193,405
Gross Unrealized Gain		1,275	507
Gross Unrealized Loss		(8,521)	(10,373)
Fair Value		135,068	183,539
Amortized Cost		41,873	45,436
Gross Unrealized Gain		0	0
Gross Unrealized Loss		(3,954)	(3,990)
Fair Value		37,919	41,446
Interest-Only-Strip, Agency CMBS [Member]
Debt Securities, Trading and Available-for-sale [Abstract]
Notional balance		7,814,762	9,711,981
Interest-Only-Strip, Non-Agency CMBS [Member]
Debt Securities, Trading and Available-for-sale [Abstract]
Notional balance		4,159,373	6,280,761
Non-Agency MBS
Debt Securities, Trading and Available-for-sale [Abstract]
Par Value		159	209
Fair Value		103	152
Amortized cost		159	209
Gross Unrealized Gain		0	0
Gross Unrealized Loss		(56)	(57)
Fair Value		$ 103	$ 152

[1] (1) The notional balance for Agency CMBS IO and non-Agency CMBS IO was $7,814,762 and $4,159,373, respectively, as of September 30, 2023, and $9,711,981 and $6,280,761, respectively, as of December 31, 2022.